The present invention relates to pumping fluids such as viscous crude oil from high productivity deep wells utilizing a submersible pump suspended from a rod string disposed in a production tube within the well casing.
Conventionally, the annular space between the casing and the production tubing string below the pump is sealed from the lower portion of the well formation by a packing or a gland. The production tube is perforated near the discharge side of the pump so that production fluid is advanced upwardly by the pump through the production tube and through the annular space. The pump is suspended usually from a rod string or sucker rod and there is but one operative pumping system. That is, there is no alternative flow path other than through the production tube and through the annular space simultaneously.
While arrangements of this type are operative they have the disadvantage of generating excessive down time and considerable expense when trouble develops in the well or when production diminishes. In such situations, the rod string and the suspended pump must be pulled from the well. Depending upon the difficulty it may even be necessary to pull the production tubing string.
Furthermore, it is frequently desirable when the fluid pump is of a high viscosity to maintain a supply of low viscosity fluid in the production tube for lubrication and dilution while producing high viscosity fluid, solely through the annular space.
Obviously to accomplish a change in pumping flow paths in prior art systems, it is necessary to pull the rod string and the tubing string to shift from one pumping mode to another at a substantial loss of time and with concomitant addition expense.